Multi-axis interferometer

Abstract

An apparatus includes a multi-axis interferometer for measuring changes in a position of a measurement object. The interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam, wherein each angle-measuring beam makes only a single pass to the measurement object before being combined to form the angle-measuring output beam. The interferometer is further configured to direct another set of beams derived from the progenitor input beam along different paths and then combine them to produce another output beam comprising information about changes in the position of the measurement object.

What is claimed is:  
     
       1. An apparatus comprising: 
       a multi-axis interferometer for measuring changes in a position of a measurement object,  
       the interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam, wherein each angle-measuring beam makes only a single pass to the measurement object before being combined to form the angle-measuring output beam, and  
       the interferometer is further configured to direct another set of beams derived from the progenitor input beam along respective paths and then combine them to produce another output beam comprising information about changes in the position of the measurement object.  
     
     
       2. The apparatus of  claim 1 , wherein the other set of beams comprises a first distance-measuring beam and a second distance-measuring beam and the other output beam is a distance-measuring output beam, and wherein the interferometer directs the first distance-measuring beam to make first and second passes to the measurement object and then combines it with the second distance-measuring beam to produce the distance-measuring output beam. 
     
     
       3. The apparatus of  claim 2 , wherein the interferometer comprises a non-polarizing beam-splitter positioned to receive the progenitor input beam and separate it into an angle-measuring input beam and a distance-measuring input beam, wherein the first and second angle-measuring beams are derived from the angle-measuring input beam and the first and second distance-measuring beams are derived from the distance-measuring input beam. 
     
     
       4. The apparatus of  claim 2 , wherein the interferometer is configured to overlap the first angle-measuring beam with the first distance-measuring beam during their first pass to the measurement object. 
     
     
       5. The apparatus of  claim 4 , wherein the interferometer comprises a non-polarizing beam-splitter positioned to separate the first angle-measuring beam from the first distance-measuring beam after their first pass to the measurement object. 
     
     
       6. The apparatus of  claim 2 , wherein the interferometer comprises a non-polarizing beam-splitter positioned to receive the angle-measuring output beam and separate a portion of it to define a distance-measuring input beam, wherein the distance-measuring beams are derived from the distance-measuring input beam. 
     
     
       7. The apparatus of  claim 6 , wherein the interferometer further comprises output fold optics positioned to direct the distance-measuring input beam, the output fold optics comprising an afocal system having a magnification selected to cause the first distance-measuring beam to contact the measurement object at substantially normal incidence for a range of angular orientations of the measurement object. 
     
     
       8. The apparatus of  claim 3 , wherein the interferometer comprises an angle-measuring optical assembly configured to direct the angle-measuring beams to the measurement object and a distance-measuring optical assembly configured to direct the distance measuring beams, wherein the angle-measuring optical assembly and distance-measuring optical assembly each comprise separate polarizing beam-splitters. 
     
     
       9. The apparatus of  claim 8 , wherein the distance-measuring optical assembly is configured as a high-stability plane mirror interferometer (HSPMI). 
     
     
       10. The apparatus of  claim 2 , wherein the interferometer is further configured to direct the first angle-measuring beam to make a pass to a reflective reference object after making the pass to the measurement object and before being combined with the second angle-measuring beam, and direct the second angle-measuring beam to make a pass to the reference object before making the pass to the measurement object. 
     
     
       11. The apparatus of  claim 10 , wherein the interferometer is further configured to direct the second distance-measuring beam to make first and second passes to the reference object. 
     
     
       12. The apparatus of  claim 11 , wherein the interferometer comprises: 
       a polarizing beam-splitter positioned to transmit one of each of the angle-measuring beams and the distance-measuring beams and reflect the other of each of the angle-measuring beams and the distance-measuring beams during each of the passes to the measurement and reference objects, and further positioned to recombine the angle-measuring beams to form the angle-measuring output beam and recombine the distance-measuring beams to form the distance-measuring output beam after the first and second passes; and  
       a return optical assembly positioned to receive the angle-measuring and distance-measuring beams from the polarizing beam-splitter and redirect them back to the polarizing beam splitter between the first and second passes.  
     
     
       13. The apparatus of  claim 12 , wherein the reference object comprises a plane mirror. 
     
     
       14. The apparatus of  claim 13 , wherein the interferometer further comprises the reference object. 
     
     
       15. The apparatus of  claim 13 , wherein the interferometer further comprises a quarter-wave retarder positioned between the polarizing beam-splitter and the reference object. 
     
     
       16. The apparatus of  claim 12 , wherein the measurement object comprises a plane mirror. 
     
     
       17. The apparatus of  claim 16 , wherein the interferometer further comprises a quarter-wave retarder positioned between the polarizing beam-splitter and the measurement object. 
     
     
       18. The apparatus of  claim 12 , wherein the return optical assembly comprises a half-wave retarder positioned to rotate the polarizations of the angle-measuring beams between the first and second passes. 
     
     
       19. The apparatus of  claim 18 , wherein the return optical assembly further comprises an odd number of reflective surfaces positioned for the redirecting of the angle-measuring beams back to the polarizing beam-splitter. 
     
     
       20. The apparatus of  claim 19 , wherein the return optical assembly further comprises a retroreflector positioned for the redirecting of the distance-measuring beams back to the polarizing beam-splitter. 
     
     
       21. The apparatus of  claim 12 , wherein the interferometer further comprises a non-polarizing beam-splitter positioned to receive the progenitor input beam and separate it into an angle-measuring input beam and a distance-measuring input beam, and wherein the polarizing beam-splitter is positioned to separate the angle-measuring input beam into the first and second angle-measuring beams and separate the distance-measuring input beam into the first and second distance-measuring beams. 
     
     
       22. The apparatus of  claim 12 , wherein the interferometer is configured to direct the first angle-measuring beam to overlap with the first distance-measuring beam during their first pass to the measurement object and direct the second angle-measuring beam to overlap with the second distance-measuring beam during their first pass to the reference object. 
     
     
       23. The apparatus of  claim 22 , wherein the polarizing beam-splitter is positioned to separate the progenitor input beam into a pair of overlapping beams comprising the first angle-measuring beam and the first distance-measuring beam and a pair of overlapping beams comprising the second angle-measuring beam and the second distance-measuring beam, and wherein the polarizing beam-splitter is further positioned to recombine the pairs of beams after their respective first passes to the measurement and reference objects to define an intermediate beam. 
     
     
       24. The apparatus of  claim 23 , wherein the return optical assembly is positioned to receive the intermediate beam and comprises a non-polarizing beam-splitter positioned to separate spatially the angle-measuring beams from the distance-measuring beams. 
     
     
       25. The apparatus of  claim 12 , wherein the interferometer comprises output fold optics comprising a non-polarizing beam-splitter positioned to receive the angle-measuring output beam and separate a portion of it to define a distance-measuring input beam, wherein the output fold optics are configured to direct the distance-measuring input beam to the polarizing beam-splitter, and wherein the polarizing beam-splitter is positioned to separate the distance-measuring input beam into the distance-measuring beams. 
     
     
       26. The apparatus of  claim 25 , wherein the output fold optics comprise an afocal system having a magnification selected to cause the first distance-measuring beam to contact the measurement object at substantially normal incidence for a range of angular orientations of the measurement object. 
     
     
       27. The apparatus of  claim 19 , wherein the odd number of reflective surfaces each comprise a normal in a common plane. 
     
     
       28. The apparatus of  claim 27 , wherein the odd number of reflective surfaces reflect the angle-measuring beams such that a sum of angles between incident and reflected beams at each of the reflective surfaces is zero or an integer multiple of 360 degrees, each angle measured in a direction from the incident beam to the reflected beam and having a positive value when measured in a counter clockwise direction and a negative value when measured in a clockwise direction. 
     
     
       29. The apparatus of  claim 12 , wherein the return optical assembly comprises a set of reflective surfaces positioned for the redirecting of the angle-measuring beams back to the polarizing beam-splitter, wherein the set of reflective surfaces reflect the angle-measuring beams such that a sum of angles between incident and reflected beams at each of the reflective surfaces is zero or an integer multiple of 360 degrees, each angle measured in a direction from the incident beam to the reflected beam and having a positive value when measured in a counter clockwise direction and a negative value when measured in a clockwise direction. 
     
     
       30. The apparatus of  claim 1 , further comprising a light source configured to produce the progenitor input beam and direct it into the multi-axis interferometer, the progenitor input beam comprising two components having an heterodyne frequency splitting, wherein one of each of the angle-measuring beams and the other set of beams is derived from one of the components in the input beam, and the other of each of the angle-measuring beams and the other set of beams is derived from the other of the components in the input beam. 
     
     
       31. The apparatus of  claim 30 , wherein the components of the input beam have orthogonal polarizations. 
     
     
       32. The apparatus of  claim 1 , further comprising detectors configured to receive the output beams and generate electrical signals indicative of the changes in the angular orientation of, and the distance to, the measurement object. 
     
     
       33. The apparatus of  claim 32 , further comprising a polarization analyzer positioned prior to each detector and configured to pass an intermediate polarization to those of the components in each of the output beams. 
     
     
       34. The apparatus of  claim 33 , further comprising a fiber optic pick-up for coupling each output beam to a corresponding detector after it passes through the corresponding polarization analyzer. 
     
     
       35. The apparatus of  claim 12 , wherein the interferometer further comprises an optical delay line positioned to reduce differential beam shear in the angle-measuring output beam. 
     
     
       36. The apparatus of  claim 35 , wherein the optical delay line is positioned to introduce additional path length to the second angle-measuring beam during its return from the measurement object. 
     
     
       37. The apparatus of  claim 35 , wherein the optical delay line is configured to introduce a difference in path length between orthogonally polarized components of an incident beam. 
     
     
       38. The apparatus of  claim 37 , wherein the optical delay line is positioned to receive the progenitor input beam and both of the output beams. 
     
     
       39. The apparatus of  claim 37 , wherein the optical delay line is positioned to receive the progenitor input beam and the distance-measuring output beam and the interferometer comprises a second optical delay line positioned to receive the second the angle-measuring beam during its pass to the measurement object. 
     
     
       40. The apparatus of claim of  1 , wherein the interferometer further comprises an optical delay block positioned to introduce additional path length to the second angle-measuring beam during its return from the measurement object to reduce differential beam shear in the angle-measuring output beam. 
     
     
       41. The apparatus of  claim 2 , wherein the first-mentioned angle-measuring output beam comprises information about the angular orientation of the measurement object with respect to a first rotation axis. 
     
     
       42. The apparatus of  claim 41 , wherein the interferometer is further configured to direct a third angle-measuring beam derived from the progenitor input beam to make a pass to the measurement object, direct a fourth angle-measuring beam derived from the progenitor input beam to make a pass to the measurement object, and then combine the third and fourth angle-measuring beams to produce a second angle-measuring output beam comprising information about the angular orientation of the measurement object with respect to a second rotation axis different from the first rotation axis. 
     
     
       43. The apparatus of  claim 42 , wherein the interferometer is configured to overlap the first and third angle-measuring beams during their pass to the measurement object. 
     
     
       44. The apparatus of  claim 42 , wherein the second rotation axis is orthogonal to the first rotation axis. 
     
     
       45. An apparatus comprising: 
       a multi-axis interferometer for measuring changes in an angular orientation of, and distance to, a measurement object,  
       the interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam, and  
       the interferometer is further configured to direct another set of beams derived from the progenitor input beam along respective paths and then combine them to produce another output beam comprising information about changes in the position of the measurement object,  
       wherein the interferometer comprises a non-polarizing beam-splitter positioned to receive the progenitor input beam and separate it into an angle-measuring input beam and another input beam, wherein the first and second angle-measuring beams are derived from the angle-measuring input beam and the other set of beams are derived from the other input beam.  
     
     
       46. An apparatus comprising: 
       a multi-axis interferometer for measuring changes in a position of a measurement object;  
       the interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam, and  
       the interferometer is further configured to direct another set of beams derived from the progenitor input beam along respective paths and then combine them to produce another output beam comprising information about changes in the position of the measurement object,  
       wherein during operation the first angle-measuring beam overlaps with a first one of the other set of beams during its first pass to the measurement object.  
     
     
       47. An apparatus comprising: 
       a multi-axis interferometer for measuring changes in a position of a measurement object;  
       the interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam, and  
       the interferometer is further configured to direct a first distance-measuring beam derived from the progenitor input beam to make first and second passes to the measurement object and then combine the first distance-measuring beam with a second-distance measuring beam derived from the progenitor input beam to produce a distance-measuring output beam,  
       wherein the interferometer comprises a non-polarizing beam-splitter positioned to receive the angle-measuring output beam and separate a portion of it to define a distance-measuring input beam, wherein the distance-measuring beams are derived from the distance-measuring input beam.  
     
     
       48. The apparatus of  claim 47 , wherein the interferometer further comprises fold optics positioned to direct the distance-measuring input beam, the fold optics comprising an afocal system having a magnification selected to cause the first distance-measuring beam portion to contact the measurement object at substantially normal incidence for a range of angular orientations of the measurement object. 
     
     
       49. An apparatus comprising: 
       a multi-axis interferometer for measuring changes in a position of a measurement object;  
       the interferometer is configured to receive a progenitor input beam, direct a first angle-measuring beam derived from the progenitor input beam to make a pass to a first point on the measurement object, direct a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object, and then combine the angle-measuring beams to produce an angle-measuring output beam, and  
       the interferometer is further configured to direct another set of beams derived from the progenitor input beam along respective paths and then combine them to produce another output beam comprising information about changes in the position of the measurement object,  
       wherein the interferometer comprises a polarizing beam-splitter positioned to combine the first angle-measuring beam with the second angle-measuring beam after the first angle-measuring beam makes its pass to the measurement object but before the second angle-measuring beam makes its pass to the measurement object, the combined beams defining an intermediate beam, and  
       wherein the interferometer further comprises a return optical assembly positioned to receive the intermediate beam and direct it back to the polarizing beam-splitter, the return optical assembly comprises a set of reflective surfaces positioned to reflect the intermediate beam an odd number of times in a plane defined by the incidence of the angle-measuring beams on the measurement object, and wherein the return optical assembly further comprise a half-wave plate configured rotate the polarization of each angle-measuring beam in the intermediate beam.  
     
     
       50. A method comprising: 
       directing a first angle-measuring derived from a progenitor input beam to make a pass to a first point on a measurement object;  
       directing a second angle-measuring beam derived from the progenitor input beam to make a pass to a second point on the measurement object;  
       combining the angle-measuring beams after their passes to the measurement object to produce an angle-measuring output beam, wherein each angle-measuring beam makes only a single pass to the measurement object;  
       directing another set of beams derived from the progenitor input beam along respective paths; and  
       combining the other set of beams to produce another output beam comprising information about changes in the position of the measurement object.  
     
     
       51. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising: 
       a stage for supporting the wafer;  
       an illumination system for imaging spatially patterned radiation onto the wafer;  
       a positioning system for adjusting the position of the stage relative to the imaged radiation; and  
       the apparatus of  claim 1  for monitoring the position of the wafer relative to the imaged radiation.  
     
     
       52. A lithography system for use in fabricating integrated circuits on a wafer, the system comprising: 
       a stage for supporting the wafer; and  
       an illumination system including a radiation source, a mask, a positioning system, a lens assembly, and the apparatus of  claim 1 ,  
       wherein during operation the source directs radiation through the mask to produce spatially patterned radiation, the positioning system adjusts the position of the mask relative to the radiation from the source, the lens assembly images the spatially patterned radiation onto the wafer, and the interferometry system monitors the position of the mask relative to the radiation from the source.  
     
     
       53. A beam writing system for use in fabricating a lithography mask, the system comprising: 
       a source providing a write beam to pattern a substrate;  
       a stage supporting the substrate;  
       a beam directing assembly for delivering the write beam to the substrate;  
       a positioning system for positioning the stage and beam directing assembly relative one another; and  
       the apparatus of  claim 1  for monitoring the position of the stage relative to the beam directing assembly.  
     
     
       54. A lithography method for use in fabricating integrated circuits on a wafer, the method comprising: 
       supporting the wafer on a moveable stage;  
       imaging spatially patterned radiation onto the wafer;  
       adjusting the position of the stage; and  
       monitoring the position of the stage using the method of  claim 50 .  
     
     
       55. A lithography method for use in the fabrication of integrated circuits comprising: 
       directing input radiation through a mask to produce spatially patterned radiation;  
       positioning the mask relative to the input radiation;  
       monitoring the position of the mask relative to the input radiation using the method of  claim 50 ; and  
       imaging the spatially patterned radiation onto a wafer.  
     
     
       56. A lithography method for fabricating integrated circuits on a wafer comprising: 
       positioning a first component of a lithography system relative to a second component of a lithography system to expose the wafer to spatially patterned radiation; and  
       monitoring the position of the first component relative to the second component using the method of  claim 50 .  
     
     
       57. A method for fabricating integrated circuits, the method comprising the lithography method of  claim 54 . 
     
     
       58. A method for fabricating integrated circuits, the method comprising the lithography method of  claim 55 . 
     
     
       59. A method for fabricating integrated circuits, the method comprising the lithography method of  claim 56 . 
     
     
       60. A method for fabricating integrated circuits, the method comprising using the lithography apparatus of  claim 51 . 
     
     
       61. A method for fabricating integrated circuits, the method comprising using the lithography apparatus of  claim 52 . 
     
     
       62. A method for fabricating a lithography mask, the method comprising: 
       directing a write beam to a substrate to pattern the substrate;  
       positioning the substrate relative to the write beam; and  
       monitoring the position of the substrate relative to the write beam using the interferometry method of  claim 50 .